Cross-species recombination in the haemagglutinin gene of canine distemper virus

Canine distemper virus (CDV) has high prevalence in the world dog population and poses an important conservation threat to many carnivore species. In this study, extensive phylogenetic and recombination analyses were performed on all available complete haemagglutinin gene sequences and a strain (AF178038) isolated from giant panda was identified as putative recombinant. Interestingly, the mosaic was produced by recombination between genotypes European wildlife and Asia-1 and the recombination event involves viruses infecting different host species. This finding may have important implications for the evolution of CDV.     

The fusion protein of wild-type canine distemper virus is a major determinant of persistent infection

The wild-type A75/17 canine distemper virus (CDV) strain induces a persistent infection in the central nervous system but infects cell lines very inefficiently. In contrast, the genetically more distant Onderstepoort CDV vaccine strain (OP-CDV) induces extensive syncytia formation. Here, we investigated the roles of wild-type fusion (F(WT)) and attachment (H(WT)) proteins in Vero cells expressing, or not, the canine SLAM receptor by transfection experiments and by studying recombinants viruses expressing different combinations of wild-type and OP-CDV glycoproteins. We show that low fusogenicity is not due to a defect of the envelope proteins to reach the cell surface and that H(WT) determines persistent infection in a receptor-dependent manner, emphasizing the role of SLAM as a potent enhancer of fusogenicity. However, importantly, F(WT) reduced cell-to-cell fusion independently of the cell surface receptor, thus demonstrating that the fusion protein of the neurovirulent A75/17-CDV strain plays a key role in determining persistent infection.     

Evidence of two co-circulating genetic lineages of canine distemper virus in South America

Canine distemper virus (CDV) is the etiological agent of a multisystemic infection that affects different species of carnivores and is responsible for one of the main diseases suffered by dogs. Recent data have shown a worldwide increase in the incidence of the disease, including in vaccinated dog populations, which necessitates the analysis of circulating strains. The hemagglutinin (H) gene, which encodes the major antigenic viral protein, has been widely used to determine the degree of genetic variability and to associate CDVs in different worldwide circulating lineages. Here, we obtained the sequence of the first full-length H gene of field South American CDV strains and compared it with sequences of worldwide circulating field strains and vaccine viruses. In South America, we detect two co-circulating lineages with different prevalences: the Europe 1 lineage and a new South America 2 lineage. The Europe 1 lineage was the most prevalent in South America, and we suggest renaming it the Europe 1/South America 1 lineage. The South America 2 lineage was found only in Argentina and appears related to wild CDV strains. All South American CDV strains showed high amino-acid divergence from vaccine strains. This genetic variability may be a possible factor leading to the resurgence of distemper cases in vaccinated dog populations.     

Adaptation of canine distemper virus to canine footpad keratinocytes modifies polymerase activity and fusogenicity through amino acid substitutions in the P/V/C and H proteins

The wild-type canine distemper virus (CDV) strain A75/17 induces a non-cytocidal infection in cultures of canine footpad keratinocytes (CFKs) but produces very little progeny virus. After only three passages in CFKs, the virus produced 100-fold more progeny and induced a limited cytopathic effect. Sequence analysis of the CFK-adapted virus revealed only three amino acid differences, of which one was located in each the P/V/C, M and H proteins. In order to assess which amino acid changes were responsible for the increase of infectious virus production and altered phenotype of infection, we generated a series of recombinant viruses. Their analysis showed that the altered P/V/C proteins were responsible for the higher levels of virus progeny formation and that the amino acid change in the cytoplasmic tail of the H protein was the major determinant of cytopathogenicity.     

Genetic diversity and phylogenetic analysis of the attachment glycoprotein of phocine distemper viruses of the 2002 and 1988 epizootics

To investigate the possible origin and spread of the dramatic re-emergent 2002 distemper epizootic observed among seals in Danish Waters, we have sequenced wild-type genes of the attachment (H) glycoproteins of viruses from both the 2002 and 1988 epizootics. Phylogenetic analysis of the H genes of phocine distemper virus (PDV) together with other morbilliviruses, suggests that the re-emergent 2002 PDV is more closely related to a putative recent ancestral PDV than the 1988 PDV isolates. Moreover, upsurges of distemper disease in land-living carnivores linked in time and locality to the 2002 seal epizootic in Danish Waters was investigated and determined to be caused by canine distemper virus, the closest relative of PDV, revealing no direct epidemiological link to the seal epizootics.     

Distinct cell tropism of canine distemper virus strains to adult olfactory ensheathing cells and Schwann cells in vitro

Canine distemper virus (CDV) can enter the brain via infection of olfactory neurons. Whether olfactory ensheathing cells (OECs) are also infected by CDV, and if yes, how they respond to the virus has remained enigmatic. Here, we exposed adult canine OECs in vitro to several attenuated (CDV-2544, CDV-R252, CDV-Ond, CDV-OndeGFP) and one virulent CDV strain (CDV-5804PeGFP) and studied their susceptibility compared to Schwann cells, a closely related cell type sharing the phagocytizing activity. We show that OECs and Schwann cells were infected by CDV strains albeit to different levels. Ten days post-infection (dpi), a mild to severe cytopathic effect ranging from single cell necrosis to layer detachment was noted. The percentage of infection increased during 10 dpi and viral progenies were detected in each culture using virus titration. Interestingly, CDV-2544, CDV-OndeGFP, and CDV-5804PeGFP predominantly infected OECs, while CDV-Ond targeted Schwann cells. No significant differences were found between the virulent and attenuated CDV strains. The observation of a CDV strain-specific cell tropism is evidence for significant molecular differences between OECs and Schwann cells. Whether these differences are either related to strain-specific distemper pathogenesis or support a role of OECs during CDV infection and virus spread needs to be addressed in future studies.     

Evolution of the receptor binding phenotype of influenza A (H5) viruses

Receptor specificity of influenza A/H5 viruses including human 2003-04 isolates was studied. All but two isolates preserved high affinity to Sia2-3Gal (avian-like) receptors. However, two isolates (February, 2003, Hong Kong) demonstrated decreased affinity to Sia2-3Gal and moderate affinity to a Sia2-6Gal (human-like) receptors. These two viruses had a unique Ser227-Asn change in the hemagglutinin molecule. Thus, a single amino acid substitution can significantly alter receptor specificity of avian H5N1 viruses, providing them with an ability to bind to receptors optimal for human influenza viruses. Asian 2003-04 H5 isolates from chickens and humans demonstrated highest affinity to the sulfated trisaccharide Neu5Acalpha2-3Galbeta1-4(6-HSO3)GlcNAcbeta (Su-3'SLN) receptor but, in contrast to 1997 isolates, had increased affinity to fucosylated Su-3'SLN. American poultry H5 viruses also had increased affinity to Su-3'SLN. These data demonstrate that the genetic evolution of avian influenza A(H5N1) viruses is accompanied during adaptation to poultry by the evolution of their receptor specificity.     

Evolution of canine and equine influenza (H3N8) viruses co-circulating between 2005 and 2008

Influenza virus, subtype H3N8, was transmitted from horses to greyhound dogs in 2004 and subsequently spread to pet dog populations. The co-circulation of H3N8 viruses in dogs and horses makes bi-directional virus transmission between these animal species possible. To understand the dynamics of viral transmission, we performed virologic surveillance in dogs and horses between 2005 and 2008 in the United States. The genomes of influenza A H3N8 viruses isolated from 36 dogs and horses were sequenced to determine their origin and evolution. Phylogenetic analyses revealed that H3N8 influenza viruses from horses and dogs were monophyletic and distinct. There was no evidence of canine influenza virus infection in horses with respiratory disease or new introductions of equine influenza viruses into dogs in the United States. Analysis of a limited number of equine influenza viruses suggested substantial separation in the transmission of viruses causing clinically apparent influenza in dogs and horses.     

The use of monoclonal antibodies specific for seal immunoglobulins in an enzyme-linked immunosorbent assay to detect canine distemper virus-specific immunoglobulin in seal plasma samples

A method is described for the measurement of antigen-specific immunoglobulin in seal pup plasmas. Four monoclonal antibodies (H1a, H13a, H24b and H49a) raised against grey seal (Halichoerus grypus) immunoglobulin were used in an ELISA procedure. Levels of canine distemper virus (CDV) specific macroglobulin (IgM like protein) were found to peak approximately 10 days after the first vaccination. Levels of other smaller CDV-specific immunoglobulins (IgG like protein) also increased after vaccination Using immunoblotting the CDV specific IgG-like protein reacted with a CDV protein, having a molecular weight of approximately 75 kDa.     

Immunohistochemical detection of antigens of distemper, adenovirus and parainfluenza viruses in domestic dogs with pneumonia

The lungs of 35 dogs that died in Mexico from acute or subacute pneumonia were examined immunohistochemically for canine distemper virus (CDV), canine adenovirus (CAV) and canine parainfluenza virus (CpiV), to determine their frequency and occurrence and possible associations. CDV was identified in 27 (77%) cases, CAV in 20 (57%) and CpiV in 18 (51%). The most frequent dual association was that between CDV and CpiV (five cases; 14%). All three viruses, however, were identified in the same lung in 10 cases. Immunolabelling occurred in alveolar macrophages, monocytes, pneumocytes, epithelial cells and syncytial cells. It was concluded that immunohistochemistry is a useful diagnostic tool in canine respiratory disease to complement histopathological examination.     

Microarray analysis of A549 cells infected with rabbitpox virus (RPV): a comparison of wild-type RPV and RPV deleted for the host range gene, SPI-1

A documented consequence of poxvirus infections is global inhibition of host protein synthesis and reduction in mRNA levels. We examined this mRNA decrease by infecting A549 cells, derived from a human lung carcinoma, with rabbitpox virus (RPV), or RPV deleted for the serine protease inhibitor SPI-1 (RPVDeltaSPI-1), which exhibits a growth defect on A549 cells. At various times postinfection, mRNA profiles were analyzed using Affymetrix U95AV2 microarrays. There was a decline in overall cellular mRNA levels beginning at 2.5 hpi, and by 5 hpi, mRNA levels were drastically reduced for the majority of genes. However, several mRNAs increased, including those of heat-shock genes. Finally, a comparison of host mRNA profiles of RPV- to RPVDeltaSPI-1-infected cells revealed subtle differences in mRNA levels at 5 and 12 hpi. In summary, while there was a global decrease of host mRNA levels, the induction of selected mRNAs may be required for a successful poxvirus infection.     

Cowpea mosaic virus-based chimaeras. Effects of inserted peptides on the phenotype,host range,and transmissibility of the modified viruses

Expression of foreign peptides on the surface of cowpea mosaic virus particles leads to the creation of chimaeras with a variety of phenotypes and yields. Two factors were shown to be particularly significant in determining the properties of a given chimaera: the length of the inserted sequence and its isoelectric point. The deleterious effect of high isoelectric point on the ability of chimeras to produce a systemic infection occurs irrespective of the site of insertion of the peptide. Ultrastructural analysis of tissue infected with chimaeras with different phenotypes showed that all produced particles with a tendency to aggregate, irrespective of the size or isoelectric point of the insert. Host range and transmission studies revealed that the expression of a foreign peptide did not (1) alter the virus host range, (2) increase the rate of transmission by beetles or through seed, or (3) change the insect vector specificity. These findings have implications for both the utility and the biosafety of Cowpea mosaic virus-based chimaeras.     

Viruses and the neuroendocrine system: model of murine obesity induced by cerebral infection by canine distemper virus]

It is currently well established that the nervous, endocrine and immune systems inter-communicate using biologically active soluble factors, synthesised and produced by these three systems themselves (e.g. immunomodulator effect of hormones, effect of substances secreted by immune cells on endocrine function.). In addition, these systems jointly express receptors for hormones, peptides, growth factors and cytokines. Immuno-neuroendocrine interactions therefore underlie physiological processes and their deregulation can result in various pathological states. By entering into complex relationships with the specialized and differentiated cells of these three systems viruses can alter inter-cellular communication and result in the appearance of pathological processes directly linked to these disturbances. In order to understand the role of viruses in the genesis of neuroimmunoendocrine pathologies, we have developed a cerebral infection model using canine distemper virus (CDV). In infected mice, this paramyxovirus, closely related to the human measles virus, induces early neurological pathologies (encephalitis) which are associated with active viral replication. Mice surviving the acute phase of infection exhibit motor deficits (paralysis and turning behaviour) or obesity during the viral persistence phase, despite the fact that the virus is no longer detectable. The obesity is characterised by hyperinsulinaemia, hyperleptinaemia and hyperplasia of the adipocytes, associated with decreased expression of the OB-Rb hypothalamic leptin receptor and modulated expression of hypothalamic monoamines and neuropeptides. These results support the viral "hit and run" theory, since the initial viral impact in the hypothalamus may be the origin of the changes in later immunoneuroendocrine communication. Thus, certain human neurodegenerative or neuroendocrine diseases may have a previous viral infection aetiology without it being possible to clearly identify the agent responsible.     

Substitutions of conserved amino acids in the receptor-binding domain of the spike glycoprotein affect utilization of murine CEACAM1a by the murine coronavirus MHV-A59

The host range of the murine coronavirus (MHV) is limited to susceptible mice and murine cell lines by interactions of the spike glycoprotein (S) with its receptor, mCEACAM1a. We identified five residues in S (S33, L79, T82, Y162 and K183) that are conserved in the receptor-binding domain of MHV strains, but not in related coronaviruses. We used targeted RNA recombination to generate isogenic viruses that differ from MHV-A59 by amino acid substitutions in S. Viruses with S33R and K183R substitutions had wild type growth, while L79A/T82A viruses formed small plaques. Viruses with S33G, L79M/T82M or K183G substitutions could only be recovered from cells that over-expressed a mutant mCEACAM1a. Viruses with Y162H or Y162Q substitutions were never recovered, while Y162A viruses formed minute plaques. However, viruses with Y162F substitutions had wild type growth, suggesting that Y162 may comprise part of a hydrophobic domain that contacts the MHV-binding site of mCEACAM1a.     

晚期糖化终产物受体反义 RNA 腺相关病毒载体的构建及在肾脏系膜细胞中表达

目的 构建晚期糖化终产物受体(RAGE)反义RNA腺相关病毒载体,并在大鼠肾脏系膜细胞中表达. 方法 构建腺相关病毒介导的RAGE反义RNA载体,3个质粒共转染293细胞,获得病毒原液,感染大鼠肾脏系膜细胞,流式细胞术、RT-PCR、ELISA检测重组病毒感染的细胞RAGE的表达和分泌细胞外基质的情况.结果 经酶切鉴定、序列分析显示RAGE基因片段正确完整反向插入pAAV-MCS.利用293细胞包装获得病毒原液的滴度为8.7×107VP/mL.感染重组病毒的细胞与正常细胞比较RAGE表达被抑制(48.2±6.1)%,分泌Ⅳ型胶原(ColⅣ)水平明显下降(P＜0.05).结论 成功构建具有抑制功能的RAGE反义RNA腺相关病毒载体,为进一步研究RAGE的作用机制,以及基因治疗RAGE相关疾病提供一个重要工具.     

博尔纳病病毒感染对新生大鼠脑内单胺类受体基因转录的影响

目的分析博尔纳病病毒(BDV)感染对新生大鼠脑内单胺类受体基因转录的影响。方法选择病毒滴度为2·0×106FFU/ml的BDV病毒液对新生大鼠进行颅内接种,接种量为10μl/只新生大鼠。30d后用RT-PCR和间接免疫荧光方法确定BDV感染情况;并采用半定量RT-PCR方法检测BDV感染大鼠脑组织中多巴胺2(D2)受体和5-羟色胺2α(5-HT2α)受体基因的mRNA转录情况。结果病毒接种后新生大鼠的BDV感染阳性率为88·89%。病毒感染大鼠脑组织中5-HT2α受体和D2受体基因的mRNA转录水平均明显低于对照组,差异有统计学意义。结论BDV感染可以明显抑制新生大鼠脑组织中D2受体和5-HT2α受体基因的mRNA转录,提示单胺类受体基因的转录与表达参与BDV感染的致病过程。